| Question | Answer |
| Absolute refractory period | time immediately after an action potential, when the sodium gates close and the membrane cannot produce an action potential in response to stimulation of any intensity |
| Action potential | rapid depolarization and slight reversal of the usual polarization caused by stimulation beyond the threshold |
| Active transport | protein-mediated process that expends energy to pump chemicals from the blood into the brain |
| Afferent axon | neuron that brings information into a structure |
| All-or-none law | principle stating that the size, amplitude, and velocity of the action potential are independent of the intensity of the stimulus that initiated it |
| Astrocyte (astroglia) | relatively large, star-shaped glia cell |
| Axon | single thin fiber of constant diameter that extends from a neuron |
| Axon hillock | swelling of the soma, the point where the axon begins |
| Blood-brain barrier | mechanism that keeps many chemicals out of the brain |
| Cell body (soma) | structure of a cell that contains the nucleus |
| Concentration gradient | difference in distribution of ions across a membrane |
| Dendritic spine | short outgrowth along the dendrites |
| Depolarization | reduction in the level of polarization across a membrane |
| Efferent axon | neuron that carries information away from a structure |
| Electrical gradient | difference in positive and negative charges across a membrane |
| Endoplasmic reticulum | network of thin tubes within a cell that transports newly synthesized proteins to other locations |
| Glia | type of cell in the nervous system that, in contrast to neurons, does not conduct impulses to other cells |
| Glucose | a simple sugar, the main fuel of vertebrate neurons |
| Graded potential | membrane potential that varies in magnitude and does not follow the all-or-none law |
| Hyperpolarization | increased polarization across a membrane |
| Interneuron | neuron whose axons and dendrites are entirely contained within a given structure |
| Intrinsic neuron | neuron whose axons and dendrites are all confined within a given structure |
| Local anesthetic | drug that attaches to the sodium channels of the membrane, preventing sodium ions from entering and thereby blocking action potentials |
| Local neuron | small neuron with no axon or a very short one |
| Membrane | structure that separates the inside of a cell from the outside |
| Microglia | very small neurons that remove waste materials and microorganisms from the central nervous system |
| Mitochondrion (pl.: mitochondria) | structure where the cell performs the metabolic activities that provide energy |
| Motor neuron | neuron that receives excitation from other neurons and conducts impulses from its soma in the spinal cord to muscle or gland cells |
| Myelin | insulating material composed of fats and proteins |
| Myelin sheath | insulating material that covers many vertebrate axons |
| Myelinated axon | axon covered with a myelin sheath |
| Neuron | cell that receives information and transmits it to other cells by conducting electrochemical impulses |
| Node of Ranvier | short unmyelinated section of axon between segments of myelin |
| Nucleus | structure within a cell that contains the chromosomes; also a cluster of neuron cell bodies within the CNS |
| Oligodendrocytes | glia cells that surround and insulate certain axons in the vertebrate brain and spinal cord |
| Polarization | electrical gradient across a membrane |
| Presynaptic terminal | tip of an axon, the point from which the axon releases chemicals |
| Propagation of the action potential | transmission of an action potential down an axon |
| Radial glia | type of glia cells that guides the migration of neurons and the growth of their axons and dendrites during embryological development |
| Refractory period | brief period following an action potential, when the cell resists the production of further action potentials |
| Relative refractory period | time after the absolute refractory period, when potassium gates remain open wider than usual, requiring a stronger than usual stimulus to initiate an action potential |
| Resting potential | electrical potential across a membrane when a neuron is not being stimulated |
| Ribosome | site at which the cell synthesizes new protein molecules |
| Saltatory conduction | jumping of action potentials from one node to another by the flow of positive ions |
| Schwann cell | glia cell that surrounds and insulates certain axons in the periphery of the vertebrate body |
| Selective permeability | ability of certain chemicals to pass more freely than others through a membrane |
| Sensory neuron | neuron specialized to be highly sensitive to a specific type of stimulation |
| Sodium-potassium pump | mechanism that actively transports three sodium ions out of the cell while simultaneously drawing in two potassium ions |
| Thiamine (vitamin B1) | chemical necessary for the metabolism of glucose |
| Threshold of excitation | level of depolarization at which a brief stimulation triggers a rapid, massive electrical change by the membrane |
| Voltage-gated channel | membrane channel whose permeability to sodium (or some other ion) depends on the voltage difference across the membrane |
